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Texas Instruments SN74LS240NSR
- Part No.:
- SN74LS240NSR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.209", 5.30mm Width)
- Datasheet:
-
SN74LS240NSR.pdf
- Description:
- IC BUFFER INVERT 5.25V 20SO
- Quantity:
- Payment:
- Shipping:
Inventory:13,496
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Product details
Overview
SN74LS240NSR from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for memory address and bus driving applications in TTL-based systems. It features dual 4-bit channels (1A–1Y and 2A–2Y), active-low output-enable inputs (1G, 2G/2G), 24 mA low-level output drive at 5 V, 14 ns typical propagation delay, and PNP input structure reducing DC loading on buses.
For engineers reviewing the SN74LS240NSR datasheet, SN74LS240NSR pinout, SN74LS240NSR application, or SN74LS240NSR equivalent, this device is selected for high-fan-out bus buffering where noise immunity, controlled enable timing, and legacy 5-V TTL compatibility are critical - especially in memory address latching, I/O expansion, and terminated line driving down to 133 Ω.
Technical Context
The SN74LS240NSR implements two independent 4-bit inverting buffer sections, each with separate active-low output-enable control (1G and 2G). Its PNP input stage reduces input current draw, improving fan-in capability and minimizing bus loading during steady-state operation.
Hysteresis (0.2–0.4 V) at all inputs enhances noise margin in electrically noisy environments such as industrial backplanes or memory subsystems. The 3-state outputs support bidirectional bus arbitration when paired with complementary devices, and the device operates within 4.5–5.5 V supply range with guaranteed performance across 0°C to 70°C ambient temperature.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Function | Octal inverting buffer with 3-state outputs; enables/disables two 4-bit channels independently |
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL power rails and tolerance to supply ripple |
| IOL (max) | 24 mA per output - drives heavy capacitive loads or multiple TTL inputs without external buffers |
| tPLH / tPHL (typ) | 14 ns at VCC = 5 V, RL = 667 Ω, CL = 45 pF - supports reliable operation in 30-MHz address/data bus environments |
| Input Hysteresis | 0.2–0.4 V - rejects transient noise on address or control lines in shared-bus systems |
| VIK (min) | –1.5 V - allows safe interfacing with open-collector or wired-AND logic without clamping diode damage |
| IOZL / IOZH (max) | ±20 µA - ensures minimal leakage current in high-impedance state, preserving bus integrity during disable |
Pinout & Package
SN74LS240NSR is packaged in a 20-pin SSOP (DB package), body size 7.20 mm × 5.30 mm, with gull-wing leads optimized for surface-mount assembly and thermal dissipation in dense PCB layouts.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1G | Channel 1 output enable (active low) | Controls all four 1Y outputs; must be pulled high via resistor during power-up to prevent bus contention |
| 1A1–1A4 | Channel 1 data inputs (inverting) | Accept TTL-compatible signals; PNP inputs reduce DC loading on upstream drivers |
| 1Y1–1Y4 | Channel 1 inverted outputs (3-state) | Drive memory address or data buses; high-impedance when 1G = HIGH |
| 2G/2G | Channel 2 output enable (active low) | Shared symbol for dual-enable variants; functionally identical to 2G in SN74LS240 |
| 2A1–2A4 | Channel 2 data inputs (inverting) | Independent of Channel 1; supports parallel or staggered bus timing schemes |
| 2Y1–2Y4 | Channel 2 inverted outputs (3-state) | Enable isolated buffering of secondary bus segments or peripheral interfaces |
| GND (Pin 10) | Ground reference | Common return for all logic and output currents; requires low-inductance connection to minimize ground bounce |
| VCC (Pin 20) | Positive supply | Must be decoupled locally with ≥0.1 µF ceramic capacitor near the package |
Key Features
| Feature | Design Value |
|---|---|
| Inverting 3-state buffer architecture | Enables bidirectional bus control when combined with non-inverting counterparts (e.g., SN74LS244), supporting memory read/write isolation |
| PNP input structure | Reduces input current to ≤0.2 mA (IIL), lowering cumulative loading on clock or address drivers in multi-device configurations |
| Input hysteresis (0.2–0.4 V) | Increases effective noise margin by >400 mV in real-world EMI-prone environments like telecom backplanes or motor-control I/O racks |
| 24 mA output sink capability | Drives up to 15 standard TTL loads directly, eliminating need for intermediate drivers in legacy system upgrades |
| 14 ns typical propagation delay | Meets timing closure for 25-MHz memory cycles with margin, enabling use in 8086/8088-era CPU support logic |
Applications
| Memory Address Buffering | LED Display Multiplexing |
|---|---|
Use Scenario: Driving 16-bit address lines from a microprocessor to multiple memory chips on a shared bus. IC Role / Device Role / Timing Role: Inverting 3-state buffer isolating CPU address outputs and enabling chip-select arbitration. Use Value: 24 mA sink current ensures clean signal edges across 100+ pF trace capacitance; hysteresis prevents false triggering during address transitions. |
Use Scenario: Controlling common-anode 7-segment LED displays via multiplexed column drivers. IC Role / Device Role / Timing Role: High-current sinking buffer for digit selection lines, synchronized with display controller PWM. Use Value: Fast 14 ns turn-off time minimizes ghosting; 3-state capability allows dynamic reconfiguration of display segments without hardware changes. |
| Industrial I/O Expansion | Legacy Bus Signal Re-timing |
Use Scenario: Adding 8-bit parallel digital I/O to PLC modules using ISA or STD bus derivatives. IC Role / Device Role / Timing Role: Level-shifting and fan-out buffer between microcontroller GPIO and field-side optocouplers or relays. Use Value: PNP inputs tolerate 2 V–3.3 V logic levels, enabling mixed-voltage interface; –1.5 V VIk rating protects against inductive kickback. |
Use Scenario: Restoring signal integrity on long (>15 cm), unterminated TTL bus traces in test equipment backplanes. IC Role / Device Role / Timing Role: Active repeater inserting controlled delay to meet setup/hold timing across distributed nodes. Use Value: Symmetrical tPLH/tPHL (14 ns typ.) avoids duty-cycle distortion; 133 Ω drive capability matches legacy bus termination standards. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal inverting buffer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS240N | Same logic function and electrical specs, but in 20-pin PDIP (N package); 50.6°C/W RθJA vs. 94.3°C/W for NSR | Preferred for through-hole prototyping or legacy repair; unsuitable for high-density SMT production | Select SN74LS240N only when manual soldering or socket-based testing is required. |
| SN74LS244NSR | Non-inverting octal buffer (same package); identical timing, drive, and thermal specs but opposite logic polarity | Used where signal inversion would disrupt control flow (e.g., data bus direction control, non-inverted address latching) | Choose SN74LS244NSR when system logic requires true (non-inverted) buffering without external inverters. |
Compared with SN74LS240N and SN74LS244NSR, the SN74LS240NSR provides optimal thermal performance for SMT volume production while maintaining strict functional equivalence to the original LS240 family - its SSOP footprint enables higher board density than PDIP, and its inverting behavior eliminates need for discrete inverters in address decode paths.
Availability
SN74LS240NSR is available at Aetrix Electronics and suitable for memory address buffering, LED display multiplexing, industrial I/O expansion, and legacy bus signal re-timing requiring stable component supply across extended product lifecycles.
Supply support for SN74LS240NSR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs for industrial, automotive, and communications markets.
The SN74LS240NSR belongs to TI's legacy 74LS logic family, engineered for high-reliability, low-power TTL-compatible interfacing in memory subsystems and bus-oriented applications from the 1980s onward.
FAQ
What is the logic function of the SN74LS240NSR?
The SN74LS240NSR is an octal inverting buffer with 3-state outputs, organized as two independent 4-bit sections (1A→1Y and 2A→2Y), each controlled by its own active-low output-enable input (1G and 2G). It performs true inversion (LOW input → HIGH output, HIGH input → LOW output) and enters high-impedance state when the respective G input is HIGH. This functionality is confirmed in the device's logic diagram and function table in the official TI datasheet SDLS144D.
Does the SN74LS240NSR support 3.3-V input logic levels?
Yes, the SN74LS240NSR inputs are tolerant down to 2 V and compatible with 3.3-V or 2.5-V logic inputs, as explicitly stated in the "Features" section of the TI datasheet. This allows direct interfacing with mixed-voltage systems without level-shifting circuitry, provided the input voltage remains within the specified VIH (≥2 V) and VIL (≤0.7 V) thresholds under recommended operating conditions.
What is the maximum output drive capability of the SN74LS240NSR?
The SN74LS240NSR delivers up to 24 mA of low-level output current (IOL) per channel at VCC = 4.75 V, as specified in Section 6.3 ("Recommended Operating Conditions") and verified in Section 6.5 ("Electrical Characteristics – SNx4LS24x"). This enables direct driving of 15 standard TTL loads or termination into 133 Ω lines, making it suitable for memory address bus applications with significant capacitive loading.
How does the SN74LS240NSR handle power-up sequencing?
To ensure the SN74LS240NSR outputs remain in high-impedance during power-up or power-down, both 1G and 2G pins must be tied to VCC through pullup resistors. The minimum resistor value depends on the current-sinking capability of the controlling driver, as detailed in Section 8.1 ("Overview") of the TI datasheet. Failure to do so may cause bus contention and potential damage to downstream devices.
Is the SN74LS240NSR pin-compatible with other packages in the SN74LS24x family?
The SN74LS240NSR uses the 20-pin SSOP (DB) package with standardized pinout matching other SN74LS24x variants in DB, DW, N, NS, and W packages, as shown in Figure 5 ("Pin Configuration and Functions") of the TI datasheet. Pin numbering and signal assignments (e.g., 1G, 1A1, 1Y1, GND, VCC) are identical across these packages - only mechanical dimensions and thermal characteristics differ.
SN74LS240NSR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 20-SOIC (0.209", 5.30mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Logic Type:
- Buffer, Inverting
- Number of Elements:
- 2
- Number of Bits per Element:
- 4
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SO
SN74LS240NSR FAQ
1.How can I place an order for SN74LS240NSR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS240NSR on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for SN74LS240NSR reliable?
The price and inventory of SN74LS240NSR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS240NSR is usually 5 days.
3.What payment methods are accepted for SN74LS240NSR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS240NSR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS240NSR?
SN74LS240NSR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS240NSR order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for SN74LS240NSR?
For technical support, including SN74LS240NSR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS240NSR requirements.
6.How does Aetrix verify that SN74LS240NSR is sourced from the original manufacturer or authorized distributors?
All SN74LS240NSR products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS240NSR meets industry standards.
7.What is the process for return or replacement of SN74LS240NSR?
All SN74LS240NSR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS240NSR, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The SN74LS240NSR part is unused and in its original packaging.
Return procedure for SN74LS240NSR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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